A conventional sensor device is disclosed in, for example, U.S. Pat. No. 6,593,663, the contents of which are incorporated herein by reference. The acceleration sensor includes a sensor chip for sensing acceleration by a sensor portion disposed on a substrate made of silicon or the like, and a circuit chip as a base substrate mounting the sensor chip thereon by using an adhesive film.
In this type of conventional sensor device, the sensor chip is connected to the substrate by a bonding wire. That is, the sensor chip is wire-bonded to the substrate.
The conventional sensor device described above uses a binding material made of silicon resin or the like with minimum elasticity to protect the sensor chip fixed on the substrate from stress. In this manner, the sensitivity of the sensor device is improved.
However, the modulus of elasticity of the binding material, e.g. an adhesive film, has to be 1 MPa or more in order to stably support the sensor chip when the wire is bonded on the chip.
Therefore, the sensitivity of the conventional sensor device is restricted by the modulus of elasticity of the binding material. In other words, there is a trade-off between the sensitivity of the sensor and the elasticity of the binding material in the conventional sensor device.
In other words, it is necessary to use a less elastic binding material in order to further increase the sensitivity of the sensor device. This is because the stress transfer from the substrate to the sensor chip has to be decreased by using less elastic binding material, for example, with the modulus of elasticity being 1 MPa or less.
The less elastic binding material, however, causes a problem in a wire bonding process. That is, the wire bonding process can't be stably conducted when the binding material is too low in the modulus of elasticity (too soft).